Phylogenetic Systematics oflguanine Lizards 93 



The subclavians of Conolophus exhibit neither of the patterns described by Zug for 

 other iguanines. In this taxon, the subclavians lie posterior and ventral to the origins of the 

 M. rectus capitis anterior and are thus not covered by this muscle. For these reasons I use 

 only the difference between the subclavians of Conolophus and those of all other iguanines 

 as a systematic character. 



According to Zug (1971), in Dipsosaurus and Brachylophus the dorsal aorta originates 

 dorsal to the heart (by union of the left and right systemic arches), while in other iguanines 

 it originates posterior to the heart. My observations on Dipsosaurus (n=l) and Sauromalus 

 (n=l) reveal a profound difference supporting this distinction. In Dipsosaurus the systemic 

 arches unite to form the dorsal aorta about as far posterior as the middle of the heart and the 

 anterior end of the ninth vertebra. In Sauromalus the systemic arches remain paired much 

 further posteriorly; they unite well behind the heart, near the middle of the 13th vertebra. 

 Conolophus, however, is intermediate. The dorsal aorta in this taxon originates at about 

 the level of the posterior end of the heart and the anterior end of the 1 0th vertebra. Because 

 Zug did not discuss variation within his two categories, I arbitrarily placed Conolophus 

 with those iguanines in which the dorsal aorta originates posterior to the heart. 



Finally, I note minor exceptions to some of Zug's observations. In the single 

 Dipsosaurus that I examined, the heart reaches the transverse axillary plane rather than 

 being entirely anterior to this plane. In the single Sauromalus that I examined, the coeliac 

 originates between, but separate from, the two mesenteric arteries. 



COLIC ANATOMY 



Iverson (1980) studied colic anatomy in iguanines. Variation within this group exists in the 

 presence of colic valves, irregular colic folds, circular valves, semilunar valves, and in the 

 number of colic valves. Although Iverson considered iguanine colic anatomy to be of 

 limited phylogenetic value, at least two characters seem to be potentially useful for inferring 

 phylogenetic relationships among iguanines. Nevertheless, because all of the colic 

 modifications that characterize subsets of iguanines appear to be transformations of 

 characters unique to iguanines, their polarity cannot be established by outgroup comparison 

 until certain phylogenetic relationships within iguanines are determined. For example, one 

 cannot use noniguanine outgroups to infer that colic folds are plesiomorphic relative to colic 

 valves, or vice versa, because neither condition occurs in these outgroups. 



The fact that noniguanines possess neither of the conditions found in iguanines is only 

 a problem if these conditions are homologous members of a transformation series. 

 Otherwise, each condition could be said to be lacking in the outgroups and therefore to be a 

 separate apomorphic state. If they are homologous, however, one is forced to detennine 

 the apomorphy of the alternative conditions relative to each other. I assume homology 

 between the colic valves and colic folds, because they share the common property of being 

 infoldings of the same tissue components of the colic wall (Iverson, 1980). I also assume 

 homology between circular and semilunar valves. The only difference between these two 

 morphologies is whether or not the infolded tissue extends around the entire perimeter of 



